JP5510212B2 - Nitride semiconductor laser device and manufacturing method thereof - Google Patents

Description

  The present invention relates to a nitride semiconductor laser device and a manufacturing method thereof, and more particularly to a nitride semiconductor laser device having a ridge waveguide structure and a manufacturing method thereof.

Nitride _{semiconductor, In x Al y Ga 1-} xy N (0 ≦ x, 0 ≦ y, 0 ≦ x + y ≦ 1) is formed by a compound semiconductor, a semiconductor laser device using the same, the next-generation DVD Various demands such as use for an optical disk system capable of recording / reproducing large-capacity / high-density information such as personal computers, electronic devices such as personal computers, and use for optical networks are increasing. For this reason, various structures have been proposed for the laser element structure that enable suitable control of the transverse mode, low power consumption, high output, high reliability, downsizing, and long life. ing.
In particular, in a laser device using a ridge waveguide structure, a protective film having a low refractive index is extended from the side surface of the ridge to both sides in order to perform optical confinement in the lateral mode with good controllability and reproducibility and to stabilize the horizontal transverse mode. A structure that is used as an embedded film and is in contact with an electrode on the upper surface of the ridge has been studied.
For example, a semiconductor in which a buried layer made of a dielectric film is formed on both sides of the ridge, and an electrode is formed on the surface of the semiconductor layer on both sides of the ridge from the ridge side wall through the buried film. A laser has been proposed (for example, Patent Document 1).
In addition, a method has been proposed in which a horizontal transverse mode is stabilized by introducing a gap in an electrode disposed on the side of the ridge (for example, Patent Document 2).

JP 2004-1111689 A JP 2007-109886 A

However, due to the recent miniaturization of laser elements, the ridge width has been reduced. When only the ridge upper surface is brought into contact with the electrode, the adhesion of the electrode to the semiconductor layer is reduced and voltage degradation occurs during continuous driving. There was a problem that it was easy.
In addition, when the electrode in contact with the ridge upper surface is disposed on the surface of the nitride semiconductor layer on both sides of the ridge via the buried film, the stress applied to the semiconductor layer is increased by the electrode material, and during continuous driving Current degradation is likely to occur, and light absorption increases depending on the film quality of the electrode formed on the side surface of the ridge.
The present invention has been made in view of the above circumstances, and a nitride semiconductor laser capable of preventing current or voltage degradation during continuous driving while controlling light confinement in the nitride semiconductor laser element. An object is to provide an element and a method for manufacturing the element.

The nitride semiconductor laser device of the present invention is
A substrate,
A nitride semiconductor layer stacked on the substrate and having a ridge on its surface;
A first protective film covering the nitride semiconductor layer;
A nitride semiconductor laser device including an electrode formed on the ridge and on the first protective film,
The first protective film is disposed in contact with a part or all of the nitride semiconductor layer from the top surface of the nitride semiconductor layer to the ridge base and the side surface of the ridge,
A gap defined by the first protective film and the electrode is provided at least at the base of the ridge.

Such a nitride semiconductor laser device preferably has one or more of the following requirements.
(1) The gap is disposed from the base of the ridge to the side surface of the ridge.
(2) The first protective film exposes a part of the side surface of the ridge, and the gap extends from the ridge base to the ridge side surface and is in contact with the ridge side surface.
(3) The first protective film has a refractive index smaller than that of the nitride semiconductor layer.
(4) The gap is disposed substantially parallel to the ridge in the ridge extension direction.
(5) A second gap is disposed between the first protective film and the ridge.

In addition, the method for manufacturing the nitride semiconductor laser device of the present invention includes:
(A) laminating a nitride semiconductor layer on a substrate;
(B) forming a mask pattern on the nitride semiconductor layer, and forming a ridge using the mask pattern;
(C) forming a first protective film on both side surfaces of the ridge, on the mask pattern, and on the nitride semiconductor layer exposed after the ridge formation;
(D) removing at least the mask pattern and the first protective film present on the mask pattern;
(E) A conductive layer composed of two or more multilayer films having different compositions is stacked on the nitride semiconductor layer including the ridge and the first protective film, and at least the shoulder of the outermost conductive layer from the base of the ridge. In the part corresponding to the part, a gap is partially introduced,
(F) removing a part of the conductive layer through the gap to form a gap defined by the first protective film and the conductive layer at least in the base portion of the ridge.

In such a method of manufacturing a nitride semiconductor laser element, it is preferable to have one or more of the following requirements.
(1) The conductive layer is formed by a first conductive layer and a second conductive layer having a different etching rate from the first conductive layer disposed on the first conductive layer.
(2) Forming the conductive layer by laminating a third conductive layer having an etching rate different from that of the first and second conductive layers under the first conductive layer, and after step (f), Forming a mask pattern on a top surface, a side surface of the ridge, and a partial surface of the nitride semiconductor layer on both sides of the ridge, and removing a part of the third conductive layer using the mask pattern;
(3) The conductive layer is formed by laminating a third conductive layer having a different etching rate from the first and second conductive layers under the first conductive layer, and in step (f), A portion of one conductive layer is removed to form a void, and after step (f), a mask pattern is formed on the upper surface and side surfaces of the ridge and a partial surface of the nitride semiconductor layer on both sides of the ridge. And a step of removing a part of the first conductive layer and the third conductive layer using the mask pattern.

  According to the nitride semiconductor laser device of the present invention, it is possible to provide a highly efficient and highly reliable nitride semiconductor laser device that prevents current or voltage deterioration during continuous driving while controlling light confinement. It becomes.

It is a schematic sectional drawing for demonstrating the structure of the nitride semiconductor laser element of this invention. It is a schematic sectional drawing for demonstrating the structure of another nitride semiconductor laser element of this invention. It is a general | schematic expanded sectional view (a)-(e) of the principal part for demonstrating the modification of the space | gap in the nitride semiconductor laser element of this invention. It is a general | schematic expanded sectional view (f)-(i) of the principal part for demonstrating the modification of the space | gap in the nitride semiconductor laser element of this invention. It is a general | schematic expanded sectional view (a)-(e) of the principal part for demonstrating the modification of the space | gap in the nitride semiconductor laser element of this invention. It is a schematic cross-sectional process drawing for demonstrating the manufacturing method of the nitride semiconductor laser element of this invention. It is a schematic cross-sectional process drawing for demonstrating another manufacturing method of the nitride semiconductor laser element of this invention. It is a schematic sectional drawing (a) of the principal part for demonstrating the manufacturing method of the nitride semiconductor laser element of this invention, (b). It is a schematic cross-sectional process drawing for demonstrating another manufacturing method of the nitride semiconductor laser element of this invention. It is a schematic cross-sectional process drawing for demonstrating another manufacturing method of the nitride semiconductor laser element of this invention. It is another schematic sectional drawing for demonstrating the structure of the nitride semiconductor laser element of this invention. It is another schematic sectional drawing for demonstrating the structure of the nitride semiconductor laser element of this invention.

The nitride semiconductor laser device of the present invention mainly includes a substrate, a nitride semiconductor layer, a first protective film, and an electrode.
For example, as illustrated in FIG. 1A, an n-side semiconductor layer 11, an active layer 12, and a p-side are formed on a first main surface of a substrate 10 having a first main surface and a second main surface as a nitride semiconductor layer. The semiconductor layer 13 is formed in this order. Note that the n-side and p-side semiconductor layers may be arranged in reverse. A ridge 14 is formed on the surface of the nitride semiconductor. A resonance surface is formed on an end surface in a direction substantially orthogonal to the extending direction of the ridge 14.

A first protective film 15 is formed on both sides of the ridge 14 and the upper surface of the p-side semiconductor layer 13 that is a nitride semiconductor layer from the base of the ridge 14. Here, the ridge base portion does not include the side surface of the ridge 14 but refers to the outer peripheral portion of the ridge on the upper surface of the nitride semiconductor. That is, the first protective film 15 is disposed so as to be in contact with the nitride semiconductor layer from the top surface of the nitride semiconductor layer to the base portion of the ridge and the side surface of the ridge. Note that the first protective film 15 is in contact with the nitride semiconductor layer, preferably all at least from the top surface of the nitride semiconductor layer to the base portion of the ridge and at least part of the ridge side surface.
Electrodes 7 are formed from the upper surface of the ridge 14 to both side surfaces, the base of the ridge 14, and the upper surface of the p-side semiconductor layer 13. The electrode 7 is in contact with the nitride semiconductor layer on the top surface of the ridge 14, and is disposed on the side surface of the ridge, the base portion, and the top surface of the p-side semiconductor layer 13 via the first protective film 15. However, at least at the base of the ridge, a gap 16 defined by the first protective film 15 and the electrode 7 is provided. Therefore, at the base of the ridge, the electrode 7 is disposed on the nitride semiconductor via the first protective film 15 and the gap 16. A p-side pad electrode 20 is usually formed on the electrode 7 and above.

A second protective film 19 is formed on the side surface of the nitride semiconductor layer and the exposed surface of the n-side semiconductor layer 11.
Further, the n-side electrode 21 is formed on a side different from the first main surface side of the substrate 10 on which the electrode 7 is disposed.
As shown in FIG. 9, the n-side electrode 21 may be formed on the exposed surface of the n-side semiconductor layer 11.

(Void 16 etc.)
As shown in FIGS. 2A (a), 2 (b), and 2 (e), the gap may be at least on the base of the ridge 14 on the first protective films 15 and 25, as shown in FIGS. Accordingly, the gaps 16 and 26 are defined by the first protective films 15 and 25 and the electrodes (7, 17 and 18, 27 and 28) at least at the base of the ridge 14. In other words, in the ridge base portion, the nitride semiconductor layer, the first protective film, the air gap, and the electrode are substantially arranged in this order from the bottom. Note that, as will be described later, a part of the nitride semiconductor layer, the first protective film, the electrode, the gap, and the electrode may be present in order from the bottom.
As described above, in the base portion of the ridge 14, the gap is arranged through at least the first protective films 15 and 25, so that the absorption of the laser beam by the electrode arranged thereon can be reduced. In particular, it is possible to further reduce laser light absorption by the electrode by substantially removing the electrode having poor film quality formed on the side surface of the ridge. In addition, light can be appropriately confined by the arrangement of the first protective film and the gap.

The size and shape of the gaps 16 and 26 are not particularly limited, and can be appropriately adjusted so as to be disposed at least at the base of the ridge 14. As a result, the stress applied to the interface between the first protective film and the ridge, the electrode and the first protective film, etc. can be relaxed. As a result, such stress can be effectively suppressed, and the life characteristics can be further improved.
However, the air gap may be positioned on the electrode as long as it is disposed on the first protective film at least at the base of the ridge. In other words, as described above, the nitride semiconductor laser device includes the nitride semiconductor layer, the first protective film, and the electrode, and the first protective film is formed from the top surface of the nitride semiconductor layer to the ridge base portion and the ridge. A part or all of the nitride semiconductor layer may be disposed in contact with the side surface, and a gap defined by the electrode may be provided at least at the base of the ridge.

  For example, when the electrode is formed in a laminated structure as will be described later, of the electrode materials formed on the first protective film in the ridge base portion, the first protective film is formed depending on the conditions in the void forming method. When the electrode material on the near side remains and the electrode material on the side far from the first protective film is removed, the electrode is arranged in a very thin state on the first protective film at the base of the ridge. Sometimes. Such an electrode in the state of an extremely thin film remains on the entire first protective film or in part, and does not absorb the laser light emitted from the light emitting layer even if it is disposed under the gap. In addition, no stress is applied to the nitride semiconductor layer by the electrode, and the optical confinement is not affected. Therefore, the arrangement of the voids in such a form is allowed in the present invention. In addition, even when thin-film electrodes are not arranged in visual observation such as electron microscope observation, electrode materials may be measured depending on elemental analysis such as STEM, but in such a state Arrangement of voids is allowed as well.

  For example, the size of the gap at the base of the ridge 14 on the first protective film 15 is not particularly limited, but specifically, the width of the gap (X in FIG. 2A (a)) is 150 nm. About 150 nm is mentioned, About 150 nm-about 1500 nm are preferable, About 300 nm-about 500 nm are more preferable. The thickness of the gap 16 (H in FIG. 2A (a)) is not particularly limited, and can be appropriately adjusted depending on the thickness of the electrode 7, the formation method of the gap 16, and the like.

  Further, as shown in FIGS. 2A (c) and 2B (f), the air gaps 16a and 26a may be disposed on a part of the side surface of the ridge 14 from the base of the ridge 14. In this case, the air gap may be arranged on the side surface of the ridge via the first protective film 15. Further, as shown in FIGS. 2A (d) and 2B (g), the gaps 16b and 26b may be disposed from the base of the ridge 14 to the entire side surface of the ridge 14. In this case, the air gap may be disposed on the side surface of the ridge via the first protective film 15, or may be disposed on the upper side surface in direct contact with the side surface of the ridge without the first protective film 15. Also good. The height of the gap on the side surface of the ridge 14 is not particularly limited, and may be equal to or less than the height obtained by subtracting the film thickness of the first protective film from the ridge height. These voids are preferably connected from the base portion to the side surface of the ridge 14.

  As will be described later, when the first protective film is formed by exposing part of the side surface (for example, the upper side surface) of the ridge, as shown in FIG. The ridge 14 may be in contact with the nitride semiconductor layer from the base portion to the side surface of the ridge 14 and on the upper side surface of the ridge 14. That is, you may arrange | position adjacent to the upper surface of the ridge 14. FIG.

The air gap 26b (or 16b) may extend to the upper surface of the ridge 14, but it is preferable that the air gap 26b (or 16b) does not extend to the upper surface of the ridge in consideration of reduction of the contact area between the ridge 14 and the electrode 27, adhesion, and the like.
Here, the contact height of the air gap 26b with the side surface of the ridge 14 (Z in FIG. 2B (g)) is, for example, about 10% to 70% of the height of the ridge 14 and about 20% to 40%. The degree is preferred. Specifically, when the ridge height is about 500 nm, the contact height of the voids is about 50 nm to 350 nm, and preferably about 100 nm to 200 nm. Particularly, since the height is high, the control of the size of the air gap is facilitated, and the optical confinement can be controlled effectively.

  Further, as shown in FIG. 3A, a part of electrodes (37 and 38) to be described later may have a gap B in the vicinity of the side surface of the ridge 14 (for example, in the vicinity of the upper side surface). In this case, the air gap 36 extends to the gap B. In FIG. 3A, the first protective film 25 exposes the side surface of the ridge 14, but may cover the entire side surface of the ridge 14.

Further, as shown in FIG. 3B, the first protective film 45 is not partly in contact with the upper end of the ridge 14 side surface, and its shape is deformed, so that the side surface of the ridge 14 of the first protective film 45 is changed. The upper end of each of the electrodes may partially contact the electrodes (47 and 48), whereby the gap 46 may be divided by the electrode 48 between the side surface of the ridge 14 and the nitride semiconductor layer.
As shown in FIG. 3C, the shape of the first protective film 55 on the side surface of the ridge 14 is deformed in the same manner as described above, and a part of the electrodes (57 and 58) has a gap near the side surface of the ridge 14. Therefore, a part of the air gap 56 may be narrowed, and a part of the air gap 56 may extend to reach the gap.

  Although not shown, these gaps preferably have a shape extending in a direction substantially parallel to the resonator direction. For example, one continuous gap may be provided in the direction of the resonator, or the gap may be divided into a plurality of gaps. With the arrangement of such voids, as described above, it is possible to reduce the laser light absorption by the electrodes arranged thereon over the extending direction of the ridge. However, it may not be arranged in all of the resonator directions, it may be arranged only in a part thereof, and there may be a portion where there is no gap in the extending direction of the ridge. That is, as shown in FIG. 3D, is the first protective film 15 covering substantially the entire side surface of the ridge 14, and the electrodes (67 and 18) are continuously adhered to the first protective film 15 to form voids? As shown in FIG. 3E, the first protective film 25 does not cover the side surface of the ridge 14, but the electrodes (77 and 28) disposed thereon are exposed surfaces of the ridge 14 and the first protective film 25. A portion that is in close contact with each other and in which no void is formed may be present in a part of the extending direction of the ridge.

  2A (a) to 2B (i) and 3 (a) to 3 (c) described above may be mixed in the extending direction of the ridge. In this case, for example, these gaps are suitably arranged at about 50% or more in the extending direction of the ridge 14, preferably about 80% or more, and arranged substantially in the direction of all the resonators. More preferably.

  The end of the gap on the resonator end face side may be closed or embedded with a protective film or the like, or may be in an open state. Therefore, the gap does not necessarily have the above-described width and height in all regions. Further, the gap may not be a complete space between the electrode and the ridge, and between the first protective film and the electrode, as long as it does not adversely affect various effects such as stress relaxation and light confinement described above. There may be a first protective film, a nitride semiconductor layer, a film residue such as a material used as a mask, and the like.

  By disposing the gap in this way, light absorption by the laser beam by the electrode or the like originally present at the site can be reduced. In addition, the refractive index difference between the gap and the ridge (nitride semiconductor) at an appropriate position effectively works to confine light efficiently in the ridge. For example, when the air gap is an air gap, the air has a minimum refractive index (1.0), and therefore there is no air gap on the side surface of the ridge (the light is confined by the difference in refractive index between the ridge and the protective film). As compared with the above, the refractive index difference between the inside and outside of the ridge is increased, and the light confinement in the ridge can be strengthened. In addition, by having a void, for example, even if a material whose refractive index is likely to fluctuate with respect to heat is adopted for the first protective film, it is less susceptible to changes in the refractive index. Can be trapped. Thereby, a threshold value can be lowered, and a reduction in input power and an improvement in life characteristics can be achieved.

Moreover, since the stress due to the close contact between the side surface of the ridge and the electrode can be reduced with respect to the ridge or the nitride semiconductor layer due to the air gap, it is possible to reduce current deterioration particularly during continuous driving.
Furthermore, since the electrode is arranged not only on the top surface of the ridge but also on the first protective film, it is possible to ensure adhesion with the ridge at the portion where the first protective film is in contact, In particular, voltage degradation during continuous driving can be reduced.
In addition, since the first protective film made of a stable material is disposed on the ridge side surface, there is little risk of deterioration such as oxidation of the nitride semiconductor layer on the ridge side surface, and stability of characteristics during operation can be achieved. .
Furthermore, heat may be trapped in the gap due to the influence of heat from the light emitting part, but since the gap is separated from the light emitting part, it is not easily affected by heat. Further, since the gap is in contact with the electrode, heat generated in the vicinity of the ridge can be efficiently radiated through the electrode.

(Nitride semiconductor layers 11, 12 and 13)
As the nitride semiconductor layer, a semiconductor layer of the general formula _{In x Al y Ga 1-xy} N (0 ≦ x ≦ 1,0 ≦ y ≦ 1,0 ≦ x + y ≦ 1). In addition to this, a group III element partially substituted with B may be used, or a group V element partially substituted with P and As may be used. The n-side semiconductor layer contains at least one of group IV elements such as Si, Ge, Sn, S, O, Ti, Zr, and Cd, group VI elements, and the like as n-type impurities. The p-side semiconductor layer contains Mg, Zn, Be, Mn, Ca, Sr, etc. as p-type impurities. The impurities are preferably contained in a concentration range of, for example, about 5 × 10 ¹⁶ / cm ³ to 1 × 10 ²¹ / cm ³ .

The nitride semiconductor layer has a light guide layer that constitutes an optical waveguide between the n-side semiconductor layer and the p-side semiconductor layer, thereby providing an SCH (Separate Confinement Heterostructure) structure that is a separated light confinement structure with an active layer interposed therebetween. It is preferable to do. However, the present invention is not limited to these structures.
The active layer may have either a multiple quantum well structure or a single quantum well structure. The active layer preferably has a smaller band gap energy than a first protective film described later. The COD level can be further improved by widening the band gap energy of the end face, in other words, widening the impurity level near the resonator face and forming a window structure.

  A ridge formed on the surface of a nitride semiconductor layer, for example, a p-side semiconductor layer, functions as a waveguide region. The width of the ridge is about 1.0 μm to 50.0 μm. Furthermore, when the beam shape is a single mode, the width of the ridge is preferably about 1.0 μm to 3.0 μm. The ridge height can be appropriately adjusted depending on the film thickness, material, and the like of the layer constituting the p-side semiconductor layer, and examples thereof include 0.1 to 2 μm. The ridge is preferably set so that the length in the resonator direction is about 100 μm to 2000 μm. The ridges may not all have the same width in the resonator direction, or the side surfaces thereof may be vertical or tapered. The taper angle in this case is suitably about 60 to 90 °.

  In the nitride semiconductor layer, for example, a resonator is formed in the direction in which the ridge extends, and a pair of resonator surfaces are formed orthogonal to the direction. Examples of the resonator surface include M-axis, A-axis, C-axis, and R-axis orientation, that is, M-plane (1-100), A-plane (11-20), C-plane (0001), or R-plane ( The surface is preferably selected from the group consisting of 1-102). The resonator surface here usually means a region including an optical waveguide region or a region corresponding to NFP, but may include a region other than the optical waveguide region or NFP.

(Substrate 10)
The substrate in the nitride semiconductor laser device of the present invention may be an insulating substrate or a conductive substrate. In the case of an insulating substrate, a part of the nitride semiconductor layer is removed in the thickness direction to expose the n-side semiconductor layer, and an n-electrode described later can be disposed so as to be in contact with the exposed surface ( (See FIG. 9). In the case of a conductive substrate, the n-electrode can be arranged so as to be in contact with the surface opposite to the surface on which the nitride semiconductor layer is formed (see FIGS. 1A, 1B, and 8).
In particular, the substrate is preferably a nitride semiconductor substrate having an off angle of about 0 ° to 10 ° on the first main surface and / or the second main surface, for example. The film thickness is, for example, about 50 μm to 1 mm.

(First protective film 15 etc.)
In the nitride semiconductor laser device of the present invention, as described above, the first protective film 15 is formed over the surface of the nitride semiconductor layer and the side surface of the ridge. In other words, the first protective film 15 is formed on the surface of the nitride semiconductor layer by exposing at least the upper surface of the nitride semiconductor layer in a region where the electrode is in direct contact with the ridge to be electrically connected (FIG. 1A). FIG. 1B and FIG. 2A (a) to (d)). The first protective film 15 may be formed so as to expose a part of the side surface (for example, the upper side surface) in addition to the upper surface of the ridge 14 (FIGS. 2A (e) and 2B (g)). And FIG. 3 (a)-(c) reference). Further, the first protective film 15 may not be in contact with all of the ridge base portion and the side surface of the ridge (this non-contact portion may be referred to as a second gap. 16aa in FIG. 2B (h), (See 26bb in FIG. 2B (i)). In addition, in the site | part which the 1st protective film is contacting the nitride semiconductor layer, both are adhering favorably. In addition, the first protective film 15 disposed on the side surface of the ridge 14 is preferably formed to be thinner than the thickness of the first protective film disposed on the surface of the nitride semiconductor layer on both sides of the ridge 14.

The second gap can be formed by known dry or wet etching. By forming the second gap, the stress applied to the interface between the first protective film and the ridge can be effectively suppressed, and the life characteristics can be further improved. In addition, the optical confinement can be stabilized by the second gap.
The size of the second gap is not particularly limited, and may be any size as long as it effectively acts on the above-described light confinement and can contribute to stress relaxation. Alternatively, the width and / or height and / or volume may be smaller than that.

  The first protective film is usually formed of an insulating material having a refractive index smaller than that of the nitride semiconductor layer. The refractive index is a spectroscopic ellipsometer using ellipsometry. A. It can be measured using HS-190 manufactured by WOOLLAM. For example, the first protective film is made of an oxide film such as Zr, Si, V, Nb, Hf, Ta, Al, Ce, In, Sb, or Zn, or an insulating film or dielectric film such as a nitride film. Examples thereof include a layer or a laminated structure. In addition, by controlling the film quality of the first protective film, it can be easily formed or processed and arranged at the above-described site. Therefore, it is preferable that the first protective film is a single crystal, a polycrystalline amorphous film, or a film partially in these crystalline states.

  Thus, by forming the first protective film from the lower surface of the ridge to the nitride semiconductor surface on both sides of the ridge, a refractive index difference with respect to the nitride semiconductor layer, particularly the p-side semiconductor layer, is ensured. Light leakage from the active layer can be controlled, light can be efficiently confined in the ridge, insulation on both sides of the ridge can be further secured, and generation of leakage current can be avoided. .

  Although the thickness of the first protective film is not particularly limited, it is appropriate to set the thickness within the range of, for example, about 10 to 2000 nm, and further within the range of 10 to 500 nm depending on the portion. By increasing the thickness of the first protective film, the capacity can be further reduced. Note that the first protective film preferably has a uniform film thickness in a region other than the side surface of the ridge. This makes it easier to control the capacity.

(Electrodes 7, 17 and 18 etc.)
Electrodes 7, 17 and 18 are formed on the upper surface of the ridge. This electrode is in contact with and electrically connected to the upper surface of the ridge 14, and the ridge 14 has a ridge 14 on the side surface of the ridge 14 with or without the first protective film 15 and partially with a gap 16 or the like. 14 side surfaces and the surface of the nitride semiconductor layer 13 are covered. However, this electrode does not need to have such a configuration over the entire extending direction of the ridge. That is, the ridge side surface may not be covered (partially divided) in a part of the ridge extension direction, and may be disposed over the entire surface of the ridge side surface via the first protective film. It may be disposed in direct contact with the side surface of the ridge, and there may be no gap between the first protective film. As described above, since the electrode is disposed up to the ridge side surface or on the nitride semiconductor layer on both sides of the ridge, the first protective film formed on the ridge side surface can be effectively prevented from peeling off. .

  The electrode here refers to an electrode formed for the purpose of at least making so-called ohmic contact with the nitride semiconductor layer, and this electrode may be a single layer (for example, 7 in FIG. 1A), but 2 A laminated structure of more than one layer (for example, 17 and 18 in FIG. 1B) is preferable, and a laminated structure of three or more layers (for example, 40, 41, and 43 in FIG. 4A (f)) is more preferable. . In this case, all the layers of the laminated structure electrode may not have the same planar shape, and one or more layers in the laminated structure may have a different planar shape from the other layers.

The electrode may be a single layer as described above, or may have a laminated structure of two or more layers, but some of the layers may not have a clear layer structure. For example, the electrode is formed by forming two conductive layers. However, the conductive layer may be alloyed, unevenly distributed, or deformed by subsequent heat treatment or the like, and may be changed into a thin film shape or an island shape. .
Accordingly, when the electrode defines a gap together with the first protective film at the base of the ridge 14, the first protective film, the electrode arranged in an island shape or the like on the first protective film, and the first protective film The gap is defined by the electrode and the like existing through the gap. In other words, in the ridge base portion, there may be a portion that is partially disposed in the order of the nitride semiconductor layer, the first protective film, the electrode, the gap, and the electrode.
As described above, when the gap is defined by the electrode at least in the ridge base, what is an ultrathin film when the electrode is disposed in a very thin state on the first protective film in the ridge base? As described above, the thickness does not affect light absorption, stress application to the nitride semiconductor layer, light confinement, and the like. Specifically, in the electrode material described later, it is suitable that the thickness is about 50 nm or less.
Further, a pad electrode or the like may be formed on this electrode.

  The electrode is formed of a single layer film or a laminated film of a metal or an alloy such as palladium, platinum, nickel, gold, titanium, tungsten, copper, silver, zinc, tin, indium, aluminum, iridium, rhodium, and ITO. Can do. Examples of the p electrode include Ni—Au (for example, 10 nm to 200 nm thickness), Ni—Au—Pt (for example, 10 nm to 100 nm to 100 nm thickness), Pd—Pt, Ni—Pt electrode material, and the like. It is done. The film thickness of an electrode can be suitably adjusted with the material etc. to be used, for example, about 50-500 nm is suitable.

(Other configurations)
A second protective film 19 is preferably formed in a partial region on the first protective film 15. The second protective film 19 preferably further covers the side surfaces of the nitride semiconductor layers 11, 12 and 13 and / or the surface or side surfaces of the substrate 10. Examples of the second protective film 19 include oxides such as Si, Mg, Al, Hf, Nb, Zr, Sc, Ta, Ga, Zn, Y, B, and Ti. Among them, an Al ₂ O ₃ or SiO ₂ film is used. Is preferred. The second protective film 19 may be the same material as the first protective film 15 or a different material. Thereby, not only the insulating property but also the exposed side surface or surface of the nitride semiconductor layer can be reliably protected. The second protective film 19 may have either a single layer structure or a laminated structure. Specifically, a single layer of an Si oxide, a single layer of an Al oxide, a stacked structure of an Si oxide and an Al oxide, or the like can be given. By forming such a film, the first protective film can be more firmly adhered to the resonator surface. As a result, stable operation can be ensured and the COD level can be improved.

  The film thickness of the 2nd protective film 19 is not specifically limited, For example, about 100-1000 nm is suitable. More preferably, it is the same material as the first protective film. Thereby, since the thermal expansion coefficient of a 1st protective film and a 2nd protective film corresponds, it can suppress that a crack generate | occur | produces in a 1st protective film and a 2nd protective film.

(Manufacturing method of nitride semiconductor racer element)
The following method is mentioned as a manufacturing method of the nitride semiconductor laser element of this invention.
(A) Formation of Nitride Semiconductor Layer First, as a substrate, for example, a nitride semiconductor substrate having an off angle of about 0 to 10 ° on the first main surface and the second main surface is prepared.
The nitride semiconductor substrate is formed by a gas phase such as MOCVD (metal organic chemical vapor deposition), MOVPE (metal organic chemical vapor deposition), HVPE (hydride vapor deposition), MBE (molecular beam epitaxy), etc. It can be formed by a growth method, a hydrothermal synthesis method in which crystals are grown in a supercritical fluid, a high pressure method, a flux method, a melting method, or the like. Further, for example, known substrates such as various substrates exemplified in JP-A-2006-24703, commercially available substrates, and the like may be used.

A nitride semiconductor layer is grown on the first main surface of the nitride semiconductor substrate.
The nitride semiconductor layer is preferably formed of an n-side semiconductor layer, an active layer, and a p-side semiconductor layer in this order or in the reverse order.
The method for growing the nitride semiconductor layer is not particularly limited, but any method known as a method for growing a nitride semiconductor, such as MOCVD, MOVPE, HVPE, MBE, can be preferably used. In particular, MOCVD is preferable because it can be grown with good crystallinity. Specifically, a method of growing under reduced pressure to atmospheric pressure conditions by MOCVD method or the like can be mentioned.

The n-side semiconductor layer is preferably formed of a multilayer film. For example, the first n-side semiconductor layer is Al _x Ga _1-x N (0 ≦ x ≦ 0.5), preferably Al _x Ga _1-x N (0 <x ≦ 0.3). Specific growth conditions include a growth temperature in the reactor of 1000 ° C. or higher and a pressure of 600 Torr or lower. The first n-side semiconductor layer can function as a cladding layer. A film thickness of about 0.5 to 5 μm is appropriate.
The second n-side semiconductor layer can function as a light guide layer and can be formed of Al _x Ga _1-x N (0 ≦ x ≦ 0.3). The film thickness is suitably 0.5-5 μm.

The active layer preferably has a general formula In _x Al _y Ga _1-xy N (0 <x ≦ 1, 0 ≦ y <1, 0 <x + y ≦ 1) containing at least In. Increasing the Al content enables emission in the ultraviolet region. Further, light emission on the long wavelength side is possible, and light emission from 360 nm to 580 nm can be performed. Luminous efficiency can be improved by forming the active layer with a quantum well structure.

A p-side semiconductor layer is stacked on the active layer. Examples of the first p-side semiconductor layer include Al _x Ga _1-x N (0 ≦ x ≦ 0.5) containing p-type impurities.
The first p-side semiconductor layer functions as a p-side electron confinement layer.
The second p-side semiconductor layer is Al _x Ga _1-x N (0 ≦ x ≦ 0.3), and the third p-side semiconductor layer is Al _x Ga _1-x N (0 ≦ x ≦ 0.5). The third p-side semiconductor layer preferably has a superlattice structure made of GaN and AlGaN, and functions as a cladding layer.
The fourth p-side semiconductor layer can be formed of Al _x Ga _1-x N (0 ≦ x ≦ 1) containing p-type impurities. In these semiconductor layers, In may be mixed. Note that the first p-side semiconductor layer and the second p-side semiconductor layer can be omitted. The thickness of each layer is suitably about 3 nm to 5 μm.

  Note that the n-side semiconductor layer and the p-side semiconductor layer may have a single film structure, a multilayer film structure, or a superlattice structure including two layers having different composition ratios. In the case of a multilayer film structure or a superlattice structure, all layers of the n-side semiconductor layer and the p-side semiconductor layer do not necessarily contain an n-type impurity and a p-type impurity.

Optionally, the nitride semiconductor layer may be etched to expose the n-side semiconductor layer (eg, the first n-side semiconductor layer). The exposure can be performed, for example, by a RIE (reactive ion etching) method using a chlorine-based gas such as Cl ₂ , CCl ₄ , BCl ₃ , or SiCl ₄ gas. Thereby, stress can be relieved. When the n-side semiconductor layer is exposed, the resonator surface may be formed simultaneously by etching. However, the formation of the resonator surface may be performed in a separate process by cleavage.
In any subsequent stage, it is preferable to anneal the obtained substrate in a nitrogen atmosphere at a temperature of about 700 ° C. or higher to lower the resistance of the p-side semiconductor layer.

(B) Formation of Ridge A mask pattern corresponding to the ridge shape is formed on the nitride semiconductor layer, and a ridge is formed using this mask pattern.
The mask pattern can be formed into an arbitrary shape by using a known method such as photolithography and an etching process using an oxide film such as SiO _{2 and} a nitride such as SiN. The film thickness of the mask pattern is suitably such that the mask pattern remaining on the ridge after the ridge is formed can be removed by a lift-off method in a later step. For example, about 0.1-5.0 micrometers is mentioned. For example, the mask pattern is preferably formed using a CVD apparatus or the like. Further, it is preferable to etch the mask pattern into an arbitrary shape by using the RIE method or the like. For the etching, it is suitable to use the above-described chlorine-based gas using the RIE method.

  Thereafter, a ridge is formed by etching the surface of the nitride semiconductor layer using the mask pattern. Etching is performed using the RIE method, for example, using the above-described chlorine-based gas. The substrate temperature at the time of etching is not particularly limited, but is preferably a low temperature (for example, about 60 to 200 ° C.).

(C) Formation of first protective film A first protective film is formed on the nitride semiconductor layer including the ridge. In this case, it is preferable to form the first protective film on the nitride semiconductor layer in a state where the mask pattern used when forming the ridge is left as it is.

  The first protective film can be formed by a method known in the art. For example, evaporation method, sputtering method, reactive sputtering method, ECR plasma sputtering method, magnetron sputtering method, ion beam assisted evaporation method, ion plating method, laser ablation method, CVD method, spray method, spin coating method, dip method or Various methods such as a method of combining two or more of these methods, or a method of combining these methods and heat treatment can be used. In this case, an arbitrary material can be used to form a single layer or a stacked structure with an arbitrary film thickness.

  By controlling the film formation method, film formation conditions, etc. of the first protective film here and appropriately selecting the material, the film thickness on the ridge side surface is reduced to the surface of the nitride semiconductor layer in the region other than the ridge side surface. It is preferable to form the film so as to be thinner than the film thickness.

The first protective film is preferably a film-like thin film that is easily lifted off at a portion corresponding to a shoulder portion of the ridge (near the ridge side surface, that is, a portion extending from the side surface of the ridge to the upper surface). In this case, the side surface of the ridge can be easily exposed by a process described later.
For example, a single-layer film may be formed once or twice or more by changing the manufacturing method or conditions, but the film may have a different thickness depending on the film quality and site, although the composition is the same. Specifically, the first protective film formed by the magnetron sputtering method can have an etching rate higher than that of the first protective film formed by the ECR sputtering method, and in particular, a film having a different film thickness on the side surface of the ridge. Can be easily formed.

Further, the first protective film formed by the ECR sputtering method has poor film quality at the protruding corner portion of the nitride semiconductor layer, and only that portion is easily lifted off, and such a first protective film can be used.
After the manufacture of the nitride semiconductor laser device, the first protective film is formed so that the second gap is formed in the ridge base portion and part of the ridge side surface from the upper surface of the nitride semiconductor layer as a result. Also good. As such a forming method, a film quality that is easy to be etched is arranged in a part of the film, a partial treatment is performed on the surface of the nitride semiconductor before forming the first protective film, and the first protective film is partially formed The method of processing to these, combining these, etc. are mentioned.

(D) Removal of first protective film At least the mask pattern and the first protective film existing on the mask pattern are removed. For example, by applying the mask pattern used for forming the ridge to the lift-off method, the mask pattern located above the upper surface of the ridge and the first protective film thereon can be removed.

At this time, by selecting an etchant to be used for lift-off, sequentially using different types of etchants, adjusting the etchant concentration, adjusting the etching time, etc., the mask pattern and the first protection immediately above it are provided. The film can be removed. Further, not only the first protective film directly above the mask pattern but also the first protective film may be removed so that the side surface of the ridge is exposed from the first protective film. Further, as described above, the mask pattern and the first protective film present immediately above the mask pattern may be removed by making the ridge side surface different from the thin film and / or the film quality of the ridge shoulder, etc. In addition to the first protective film directly above the first protective film, a part of the first protective film existing on the ridge shoulder portion or the side surface portion of the first protective film may be removed. In addition, after the lift-off method, the first protective film corresponding to the shoulder portion of the ridge may be removed by separate etching, optionally using a mask pattern.
In addition, it is preferable that at least a part of the side surface of the ridge is covered and adhered without removing the first protective film on the lower surface of the ridge. Thereby, peeling of the first protective film can be effectively prevented.

(E) Lamination of conductive layers On the obtained nitride semiconductor layer and the first protective film, a single-layer conductive layer or a conductive layer composed of two or more multilayer films having different compositions is laminated. In the case of laminating a conductive layer made of a multilayer film, for example, it is preferable to select multilayer films having different etching rates according to a predetermined etching method and conditions. At this time, it is suitable to partially introduce a gap into at least the conductive layer on the outermost surface and corresponding to the base portion to the shoulder portion of the ridge.

  The method for forming the conductive layer is not particularly limited. For example, in the case of a single layer structure made of Au, Au is formed with a film thickness of about 50 to 300 nm. For example, in the case of a two-layer structure composed of Ni and Au, first, Ni is formed with a thickness of about 5 to 20 nm on the nitride semiconductor layer, and then Au is formed with a thickness of about 50 to 300 nm. To do. In the case of a two-layer structure composed of Au and Pt, first, Au is formed with a thickness of about 50 to 200 nm on the nitride semiconductor layer, and then Pt is formed with a thickness of about 50 to 200 nm. Further, when the p-electrode has a three-layer structure, it is preferable to form Ni—Au—Pt or Ni—Au—Pd in this order. For example, Ni is formed with a thickness of 10 nm, Au is formed with a thickness of 100 nm, and Pt or Pd that is the outermost surface layer is formed with a thickness of about 50 to 500 nm. Furthermore, Rh, Pd, Ag, Pt, Au, and the like may be formed in any film thickness in any film thickness and in any film formation method at any position. However, when the conductive layer is formed of three or more layers, all of them may have different etching rates, but not all of them need to have different etching rates, and the composition differs between at least two conductive layers. Or the thing from which an etching rate differs is preferable.

  The film forming method can be formed by a method known in the art. For example, vapor deposition, sputtering, reactive sputtering, ECR plasma sputtering, magnetron sputtering, ion beam assisted deposition, ion plating, laser ablation, CVD, or a combination of two or more of these methods Various methods can be used. In this case, it is preferable that an arbitrary material is used and an arbitrary film thickness is selected and an arbitrary condition is selected.

  When a gap is partially introduced into the portion corresponding to the shoulder from the base of the ridge of the ridge of the outermost surface simultaneously or continuously with the lamination of the conductive layer, for example, (i) the conductive layer is formed by the above-described method. And a method of forming a mask pattern having an opening in a portion corresponding to the gap and performing wet or dry etching using the mask pattern. Further, (ii) such a mask pattern may be arbitrarily used to select an angle at which the conductive layer can be partially thinned, and the conductive layer may be sputtered to partially introduce a gap.

  Furthermore, (iii) when forming the conductive layer described above, by changing the conditions such as increasing the film formation rate, the uppermost conductive layer is formed in a poor film quality, or a gap is introduced ( iv) A method of introducing a gap by partially etching the uppermost conductive layer by forming the uppermost conductive layer in a poor film quality, (v) Conditions or materials when forming the uppermost conductive layer. And a method of partially introducing a gap from the shoulder portion of the ridge to the uppermost conductive layer portion corresponding to the base portion using the presence or absence of the first protective film as a base, (vi ) When forming the ridge, adjust the inclination angle of the side surface of the ridge so that a gap can be introduced from the shoulder portion of the ridge to the portion of the uppermost conductive layer corresponding to the base portion by a normal method of forming a conductive layer Various methods such as a method can be used.

These methods can be realized by using a method known in the art depending on the apparatus, conditions, materials, and the like to be used. Thereby, for example, as shown in FIGS. 5A and 5B, a plurality of gaps 22 and 23 can be introduced in the uppermost conductive layer 43.
In this case, for example, as shown in FIG. 5B, by introducing the gap 23 only in the vicinity of the base portion of the uppermost conductive layer 43 (or the outermost surface of the conductive layer), the post-process shown in FIG. A gap can be formed at the position shown in a) or FIG. 2A (b) and FIG. 2A (e).
Further, as shown in FIG. 5A, by introducing the gap 22 also in the vicinity of the shoulder portion of the uppermost conductive layer 43, in the subsequent step, FIG. 2A (c), FIG. 2A (d), FIG. Gaps can be formed at the positions shown in (f) and FIG. 2B (g).
The size and density of the gap in this case are not particularly limited, but it is preferable that the gap has a thickness and a film formation area that can finally function as an electrode. Note that such a film formation method for introducing a gap may be used not only for forming the uppermost layer but also for forming a conductive layer disposed in a lower layer.

The electrode in contact with the top surface of the ridge is formed by stacking the conductive layers described above. Any known method may be used as the electrode forming method in this case. For example, a conductive layer other than the uppermost layer among the conductive layers having a laminated structure is formed, and then a lift-off pattern having an opening only at an electrode forming portion is formed, and then the uppermost conductive layer is formed thereon and lift-off is performed. The method attached to a law is mentioned. Thus, the uppermost layer can be patterned into an electrode having a desired shape, and the patterned conductive electrode can be used as a mask to further pattern the lower conductive layer to form an electrode having a desired shape.
Further, before forming the conductive layer, a lift-off pattern having an opening only at the electrode forming portion is formed, and a conductive layer having a multilayer structure is formed thereon, and then the conductive layer having the multilayer structure is subjected to a lift-off method. Thus, a method of forming an electrode having a desired shape may be used.

  Therefore, it is preferable to pattern the stacked conductive layer into a desired electrode by appropriately combining the above-described method of forming a conductive layer having a stacked structure and forming a gap in the uppermost layer with the above-described electrode forming method.

(F) Formation of voids Using the gap of the uppermost layer (or outermost surface) of the conductive layer described above, a single-layer conductive layer is positioned at a part of the inside, and a stacked-layer conductive layer is positioned below it. Part of the conductive layer is removed. As a result, a gap defined by the first protective film and the conductive layer can be formed at least at the ridge base.
Such a part of the conductive layer can be removed by known dry or wet etching. For example, an HF (hydrofluoric acid) solution, a BHF (buffered hydrofluoric acid) solution, a hydrochloric acid solution such as a mixed solution of hydrochloric acid and acetic acid, a solution having an oxidizing action such as nitric acid or hot concentrated sulfuric acid, aqua regia, It is appropriate to carry out by wet etching, lift-off method, or dry etching using chlorine-based gas, etc., by mixing one or two or more of iodine-iodide-based solutions or using two or more in turn. is there. At this time, as described above, the gap in the uppermost (or outermost) conductive layer is used, and the material, film thickness, stacked structure, film formation method, etching method, etchant type, and etchant of the lower conductive layer are used. Etching is performed so as to form a gap adjacent to a part of the side surface of the ridge by appropriately adjusting various conditions such as the concentration and etching time.

  If the first protective film remains without exposing the side surface of the ridge, the next step may be performed as it is. However, the material of the first protective film, the film quality, the film thickness, the material of the above-described lower conductive layer, etc. are appropriately selected. By doing so, the first protective film may be removed so that a part of the ridge side surface of the first protective film is exposed simultaneously with the removal of the conductive layer. At this stage, the shape and size of the gap can be adjusted by adjusting various parameters such as the inclination angle of the ridge, the type of etchant, the concentration, and the processing (soaking) time. Specifically, when Ni is contained in the lower layer, Ni can be etched with a hydrochloric acid-based solution such as a mixed solution of hydrochloric acid and acetic acid, and Rh, Pd, and Ag are nitric acid-based. Alternatively, etching can be performed with a hot concentrated sulfuric acid solution, etc., Pt can be etched with aqua regia, etc., and Au can be etched with potassium iodide iodide or aqua regia. Therefore, a method of selecting these materials, stacking order, and etchant appropriately is preferable.

In addition, it is a case where the conductive layer has a laminated structure of three or more layers. For example, the lowermost conductive layer (that is, the third conductive layer) is the upper conductive layer, the uppermost conductive layer. When formed of a material having a different etching rate from that of the conductive layer (that is, the second conductive layer), after the step (f), a partial surface of the nitride semiconductor layer on the top surface, side surface, and both sides of the ridge. A mask pattern may be formed thereon, and a part of the lowermost conductive layer may be removed using this mask pattern.
Further, in the step (f), when only a part of the upper conductive layer (that is, the first conductive layer) is removed and the part remains, the mask pattern described above is provided after the step (f). The upper conductive layer (that is, the first conductive layer) may be further removed together with part or all of the lowermost conductive layer (that is, the third conductive layer).
In this manner, by separately forming a mask pattern and removing a part of the conductive layer, the void can be formed more reliably without causing etching damage to the uppermost conductive layer. That is, it is possible to further promote the extension of the gap in the extension direction of the ridge and to extend the gap on the nitride semiconductor layers on both sides of the ridge.

  As a result, the removal of the conductive layer may be completely removed at the portion where the void is disposed, or may remain in the form of a thin film or an island. The remaining thickness of the conductive layer is allowed to be at least not affected by confinement of light emitted from the active layer. Further, the thickness may be such that it can be stopped to such an extent that it does not affect light confinement or the like by alloying by annealing in a later step. Specifically, although depending on the material, about 5 to 20 nm may be mentioned.

It is preferable to perform ohmic annealing at any stage such as after the formation of the multi-layered conductive layer and after the patterning of the conductive layer (formation of voids). For example, annealing conditions of about 300 ° C. or higher, preferably about 500 ° C. or higher are appropriate in an atmosphere containing nitrogen and / or oxygen.
Even in the case where the conductive layer is formed in a laminated structure in the above-described process, depending on the material, two or more layers may be alloyed to change into a single layer structure after annealing. One or more of the layers may be thinned or unevenly distributed.

A second protective film may be formed on the first protective film at an arbitrary stage after step (f).
The second protective film can be formed by a method known in the art.
Optionally, the pad electrode 20 may be formed on the electrode formed on the ridge described above. The pad electrode is preferably a laminate made of a metal such as Ni, Ti, Au, Pt, Pd, or W. Specifically, the pad electrode can be formed in the order of W—Pd—Au or Ni—Ti—Au from the electrode side. The film thickness of the pad electrode is not particularly limited, but the film thickness of the final layer of Au is preferably about 100 nm or more.

  Furthermore, another electrode may be formed on an arbitrary semiconductor layer on the first main surface of the nitride semiconductor substrate (see 21 in FIG. 9), or a part of the electrode may be formed on the second main surface of the nitride semiconductor substrate. Another electrode may be formed on the entire surface or the entire surface (see 21 in FIGS. 1A, 1B, and 8). For example, V (film thickness 10 nm), Pt (film thickness 200 nm), Au (film thickness 300 nm) can be formed from the second main surface side of the substrate. This another electrode can be formed by, for example, sputtering, CVD, vapor deposition, etc., preferably V / Pt / Au, Ti / Au / Pt / Au, Mo / Pt / Au, W / Pt / Au, A two-layer structure to a four-layer structure made of Ti / Pd / Al, Ti / Al, Cr / Au, W / Al, Rh / Al, and Ti / Pt / Au. For the formation of another electrode, it is preferable to use a lift-off method, and after forming another electrode, it is preferable to perform annealing at about 500 ° C. or higher, but annealing can be omitted. Furthermore, a metallized electrode may be formed on this other electrode. The metallized electrodes are, for example, Ti—Pt—Au— (Au / Sn), Ti—Pt—Au— (Au / Si), Ti—Pt—Au— (Au / Ge), Ti—Pt—Au—In, It can be formed of Au / Sn, In, Au / Si, Au / Ge, or the like.

(Chip formation)
At any stage, preferably after forming the electrode, the substrate containing the nitride semiconductor layer is usually divided into bars to form the cavity facet of the nitride semiconductor layer in the direction perpendicular to the ridge To do. Here, it is preferable that the resonator end face is an M plane (1-100) or an A plane (11-20). As a method of dividing the substrate including the nitride semiconductor layer into a bar shape, there is a blade break, a roller break, or a press break.

A reflection mirror may be formed on the end face of the resonator. Reflection mirror is preferably set to _{SiO 2, ZrO 2, TiO 2} , Al 2 O 3, Nb 2 O 5, AlN, dielectric multilayer film made of _Ta 2 _{O 5} or the like. The reflection mirror is preferably formed on the light reflection side and the light emission surface of the resonance surface. If the resonance surface is formed by cleavage, the reflection mirror can be formed with good reproducibility. The end face of the gap may be covered with a mirror. As a result, it is possible to prevent dust or the like from entering the gap during the subsequent process or driving of the laser, thereby reducing the function of the gap.
The nitride semiconductor substrate in the form of a bar is usually divided in parallel with the stripe direction of the electrodes to form a nitride semiconductor laser device as a chip.
Note that the second gap can be formed simultaneously with the formation of the first protective film, the formation of the first gap, the patterning or etching of the electrode, and the like.

Embodiments of a nitride semiconductor laser device and a manufacturing method thereof according to the present invention will be described below in detail with reference to the drawings.
Example 1: Nitride Semiconductor Laser Element The laser element of this example is an element that oscillates in the 500 nm band or less. As shown in FIG. 8, an n-side semiconductor layer 11 is formed on a substrate 10 made of n-type GaN. As shown, an n-side cladding layer (2 μm) made of Si-doped Al _0.33 Ga _0.67 N and an n-side light guide layer (0.15 μm) made of undoped GaN are formed. Further, as the active layer 12, a barrier layer (7 nm) made of Si-doped In _0.02 Ga _0.98 N and a well layer (10 nm) made of undoped In _0.06 Ga _0.94 N were repeated twice, A barrier layer (5 nm) made of Si-doped In _0.02 Ga _0.98 N is formed. On top of this, as a p-side semiconductor layer 13, a p-side cap layer (10 nm) made of Mg-doped p-side Al _0.30 Ga _0.70 N, a p-side light guide layer (0.15 μm) made of undoped GaN, A p-side cladding layer made of a superlattice layer having a total film thickness of 0.6 μm, a layer made of undoped Al _0.05 Ga _0.95 N (2.5 nm) and a layer made of Mg-doped GaN (2.5 nm), Mg-doped p-side GaN A p-side contact layer (15 nm) is formed.

By etching, a striped ridge 14 (inclination angle of 80 °) having a height of about 0.7 μm and a width of about 2 μm is formed on the surface of the p-side semiconductor layer.
A first protective film 25 made of ZrO ₂ is formed on the surface of the p-side semiconductor layer excluding the upper surface of the ridge 14 and the shoulder.
On the side surface of the ridge 14, a gap 26b is formed at a position adjacent thereto. The air gap 26 b is disposed on the lower side surface of the ridge 14 and part of the nitride semiconductor layer on both sides of the ridge 14 via the first protective film 25. The gap 26b has a height Z (see FIG. 2B (g)) of about 150 nm on the side surface of the ridge 14 and a width X of about 400 nm on the nitride semiconductor layers on both sides of the ridge 14.

Electrodes (27b and 28) are formed over a part of the nitride semiconductor layer on both sides of the ridge 14 from the upper surface of the ridge 14. The electrode 27b is formed by laminating a Ni film (for example, a film thickness of about 10 nm) and an Au film (for example, a film thickness of about 100 nm) in this order, and is separated by a gap 26b at a part of the side surface of the ridge 14. Has been. The electrode 28 is formed of a Pt film (for example, a film thickness of about 100 nm). A p-side pad electrode 20 is formed on the electrodes (27b and 28).
A second protective film 19 is formed on the side surface of the nitride semiconductor layer and the exposed surface of the n-side semiconductor layer 11.
Further, an n-side electrode 21 is formed on the back surface of the substrate 10.

About this semiconductor laser chip, each electrode was wire-bonded and laser oscillation was performed at room temperature. As a comparative example, it is basically the same as the semiconductor laser manufacturing method described later, but a laser element is formed so as not to introduce voids, and each electrode is similarly wire-bonded at room temperature. Laser oscillation was performed.
As a result, it was confirmed that in the laser element of this example, the driving current was reduced by about 15% compared to the laser element having no air gap, and stable operating current and operating voltage were exhibited for a long time.
Further, the laser light absorption by the electrode disposed thereon can be reduced in the extending direction of the ridge, and the light emission efficiency can be increased.

Example 2: Method for Manufacturing Nitride Semiconductor Laser Device The laser device of Example 1 can be manufactured by the following method.
(A) Formation of Nitride Semiconductor Layer First, a substrate 1 made of n-type GaN is set in a MOVPE reaction vessel, and trimethylaluminum (TMA), trimethylgallium (TMG), ammonia (NH ₃ ), silane gas (impurity gas) Using SiH ₄ ), an n-type cladding layer made of Al _0.33 Ga _0.67 N doped with Si is grown.
Subsequently, an n-side light guide layer made of undoped GaN is grown using TMG and ammonia.

Next, a barrier layer made of In _0.02 Ga _0.98 N doped with Si was grown using trimethylindium (TMI), TMG, ammonia, and silane gas. The well layer made of undoped In _0.06 Ga _0.94 N is grown by stopping the silane gas and using TMI, TMG and ammonia. After repeating this twice, a barrier layer made of In _0.02 Ga _0.98 N was grown using TMI, TMG, and ammonia, and an active layer (refractive index consisting of two pairs of multiple quantum wells (MQW)) was grown. : About 2.5). Stop TMI, use TMA, TMG and ammonia, flow biscyclopentadienylmagnesium (Cp ₂ Mg), grow a p-type cap layer made of Mg-doped p-type Al _0.30 Ga _0.70 N .

Subsequently, Cp ₂ Mg and TMA are stopped, and a p-side light guide layer made of undoped GaN is grown. Subsequently, a p-side cladding layer made of a superlattice layer having a total film thickness of 0.6 μm, consisting of a layer made of undoped Al _0.05 Ga _0.95 N (2.5 nm) and a layer made of Mg-doped GaN (2.5 nm) is grown. . Finally, a p-type contact layer made of p-type GaN doped with Mg is grown on this by flowing Cp ₂ Mg using TMG and ammonia.

(B) the ridge of forming on a substrate a wafer formed by laminating a nitride semiconductor layer, removed from the reaction vessel, the surface of the uppermost p-side contact layer, forming a mask pattern of SiO ₂ consisting of a stripe of width 2μm To do.
Thereafter, using RIE, etching is performed to the vicinity of the interface between the p-side cladding layer and the p-side light guide layer to form a striped ridge 14. At the same time, the nitride semiconductor layer is etched by RIE to expose, for example, a partial surface of the n-side cladding layer.

(C) Formation of First Protective Film Next, with the mask pattern remaining, a first protective film 25 made of a single layer of ZrO ₂ is formed on the surface of the nitride semiconductor layer using an ECR sputtering apparatus. The first protective film 25 is formed with a film thickness of 200 nm. Note that the degree of removal of the first protective film in the following steps can be adjusted by changing the film formation conditions here.

(D) Removal of first protective film The first protective film 25 formed on the p-side contact layer is removed together with the mask pattern made of SiO ₂ by a lift-off method. The removal of the first protective film 25 can be performed, for example, by wet etching using BHF, and the first protective film 25 is formed on the ridge 14 by adjusting the etching time or adjusting the concentration of BHF. Also remove some of the sides.

(E) Stacking of Conductive Layer Next, as shown in FIG. 4A (a), a conductive layer 40 made of Ni film and a conductive layer 41 made of Au film are sputtered on the p-side contact layer including the ridge 14. Laminate by the method. Further, as shown in FIG. 4A (b), a mask pattern 42 having an opening in a region corresponding to the p-side electrode is formed of a resist by photolithography and etching processes.
Thereafter, as shown in FIG. 4A (c), a conductive layer 43 made of a Pt film is formed on the conductive layers 40 and 41 including the mask pattern 42 by a sputtering method, and a conductive layer made of a Pt film is formed by a lift-off method. 43 is patterned (see FIG. 4A (d)).

  Here, although not shown, a mask pattern having an opening is formed in a part of the conductive layer 43 made of a Pt film corresponding to the shoulder portion of the ridge 14, and this mask pattern is used as a mask and using aqua regia, The gap 22 is introduced into the conductive layer 43 corresponding to the shoulder of the ridge 14 by wet etching for a relatively single time (see FIG. 5A). The introduction of the gap 22 here can be appropriately introduced by adjusting the concentration of aqua regia, etching time, and the like. At this time, the gap 23 may be introduced into the conductive layer 43 corresponding to the base portion of the ridge 14 by changing the shape of the mask pattern (see FIG. 5B), and the shoulder portion of the ridge. A gap may be introduced into the conductive layer 43 corresponding to both the base portion and the base portion.

  Subsequently, as shown in FIG. 4A (e), the conductive layer 41 made of an Au film is patterned by wet etching using a potassium iodide iodide solution as an etchant using the conductive layer 43 made of a Pt film as a mask. At this time, the conductive layer 41 made of the Au film at the portion corresponding to the base portion is also removed from the shoulder portion of the ridge 14 through the gap of the conductive layer 43 introduced earlier, and a void is introduced into the portion. .

As shown in FIG. 4A (f), a mask pattern 44 covering the conductive layer 43 made of a Pt film is formed of a resist by photolithography and etching processes.
Using this mask pattern 44 as a mask, the conductive layer 40 made of a Ni film is patterned by wet etching using a hydrochloric acid-based solution made of a mixture of hydrochloric acid and acetic acid as an etchant to form an electrode. Here, the mask pattern 44 is formed so that the conductive layer 40 formed on the upper surface of the ridge is not removed through the gap of the conductive layer 43 introduced earlier. As a result, the conductive layer 40 made of the Ni film remains on the upper surface of the ridge covered with the mask pattern 44, the side surface of the ridge, and the lower portion of the gap, and the Ni film is removed at the portion exposed from the mask pattern 44.
Thereafter, a p-side pad electrode electrically connected to the p-side electrode is formed on the electrode.

After these steps, annealing is performed at about 500 ° C. in an oxygen atmosphere in order to ensure ohmic properties. As a result, a part or all of the conductive layer 40 made of the Ni film adjacent to the gap 26b is unevenly distributed, and a portion arranged in an island shape on the first protective film 25 is formed. Further, the conductive layer 40 made of Ni film and the conductive layer 41 made of Au are alloyed, and these are partially or entirely arranged as a single layer structure.
Thereafter, an n-side electrode is formed on the back surface of the n-type GaN substrate.

After forming both the p and n electrodes in this manner, the wafer is obtained by cleaving GaN at the M surface of the GaN substrate (the surface corresponding to the side surface of the hexagonal column when the nitride semiconductor is represented by a hexagonal column). A bar shape is formed, and a resonance surface is formed on the cleavage surface of the bar. Thereafter, the bar-shaped wafer is further cut into chips in a direction perpendicular to the resonance surface.
The alloying, deformation, or uneven distribution of the conductive layer made of the Ni film described above is necessary for the obtained laser element to ensure driving current, stable operating current and operating voltage, absorption of laser light, and luminous efficiency. It has been confirmed that there is substantially no influence, and the same effect as the laser element of Example 1 can be obtained.

Example 3 Method of Manufacturing Nitride Semiconductor Laser Element The laser element of Example 1 can also be manufactured by the following method.
Step (a) The removal of the first protective film from the formation of the nitride semiconductor layer to step (d) is performed in the same manner as in Example 2.

  In the manufacturing method of this embodiment, a step portion is formed on the side surface of the ridge by removing the first protective film in the step (d), and the conductive layer is formed in the step (e) by using the step portion. Laminate to form an electrode. In the electrode formed here, a gap is introduced into a part of the conductive layer 43 due to the step portion on the side surface of the ridge.

(E) Stacking of Conductive Layer As shown in FIG. 6A, a mask pattern 52 having an opening in a region for forming a p-side electrode is formed on the nitride semiconductor layer on which the first protective film 25 is formed.
As shown in FIG. 6B, a conductive layer 50 made of a Ni film, a conductive layer 51 made of an Au film, and a conductive layer 53 made of a Pt film are sputtered on the nitride semiconductor layer including the mask pattern 52, respectively. Form and stack by the method.

As shown in FIG. 6C, patterning is performed by a lift-off method to form an electrode. At this time, a gap is introduced into the shoulder portion of the conductive layer 53 by using the step portion on the side surface of the ridge described above.
Thereafter, although not shown, the conductive layer 51 made of an Au film is etched by wet etching using a potassium iodide iodide solution as an etchant. As a result, the conductive layer 51 made of the Au film at the portion corresponding to the shoulder portion of the ridge 14 is also removed through the gap of the conductive layer 53 introduced earlier, and a void is introduced at that portion.
Thereafter, a semiconductor laser element is formed in the same manner as in the second embodiment. The obtained laser element has the same effect as the laser element of Example 1.

Example 4: Method for Manufacturing Nitride Semiconductor Laser Element The laser element of Example 1 can also be manufactured by the following method.
Step (a) The removal of the first protective film from the formation of the nitride semiconductor layer to step (d) is performed in the same manner as in Example 2.

(E) Stacking of Conductive Layer Next, as in Example 2, as shown in FIG. 4B (a), the conductive layer 40 made of Ni and the Au film are formed on the p-side contact layer including the ridge 14. The conductive layer 41 is stacked by a sputtering method. Further, as shown in FIG. 4B (b), a mask pattern 42 having an opening in a region corresponding to the p-side electrode is formed of a resist by photolithography and etching processes.
Thereafter, as shown in FIG. 4B (c), a conductive layer 43 made of a Pt film is formed on the conductive layers 40 and 41 including the mask pattern 42 by a sputtering method, and a conductive layer made of a Pt film is formed by a lift-off method. 43 is patterned (see FIG. 4B (d)).
Thereafter, as in the second embodiment, a gap is introduced into the conductive layer 43 using a mask pattern.

  Subsequently, as shown in FIG. 4B (e), the conductive layer 41 made of an Au film is patterned by wet etching using a potassium iodide iodide solution as an etchant using the conductive layer 43 as a mask. At this time, the conductive layer 41 made of the Au film corresponding to the base portion is also removed from the shoulder portion of the ridge 14 through the gap of the conductive layer 43 introduced earlier, and the gap 26b is introduced into the portion. The

Subsequently, as shown in FIG. 4B (f), by wet etching using a hydrochloric acid-based solution made of a mixture of hydrochloric acid and acetic acid as an etchant, the conductive layer 43 and the conductive layer 41 made of an Au film are used as a mask from the Ni film. The conductive layer 40 to be formed is patterned to form an electrode. At this time, the conductive layer 43 made of Ni film adjacent to the gap 26b is also removed through the gap of the conductive layer 43 introduced earlier and the gap 26b corresponding to the base portion from the shoulder portion of the ridge 14. A gap 26b 'is secured at that portion.
Thereafter, a semiconductor laser element is formed in the same manner as in the second embodiment.
In such a manufacturing method, the conductive layer made of the Ni film described above is alloyed with the conductive layer 41 made of the Au film in contact therewith by annealing. The obtained laser element has the same effect as the laser element of Example 1.

Example 5: Manufacturing Method of Nitride Semiconductor Laser Element The laser element of Example 1 can also be manufactured by the following method.
Step (a) The removal of the first protective film from the formation of the nitride semiconductor layer to step (d) is performed in the same manner as in Example 2.
In the manufacturing method of this embodiment, a step portion is formed on the side surface of the ridge by removing the first protective film in the step (d), and the conductive layer is formed in the step (e) by using the step portion. Laminate to form an electrode. In the electrode formed here, a gap is introduced into a part of the conductive layer 43 due to the step portion on the side surface of the ridge.
After that, in the same manner as in Example 2, the conductive layer 41 made of Au film is patterned using the conductive layer 43 with the gap introduced as a mask, and the conductive film made of Au film at the portion corresponding to the base portion from the shoulder portion of the ridge 14 is formed. A part of the layer 41 is removed to form a void at that portion.

Subsequently, as shown in FIG. 4A (f), a mask pattern 44 covering the conductive layer 43 made of a Pt film is formed of a resist by photolithography and etching processes.
Using this mask pattern 44 as a mask, the conductive layer 40 made of a Ni film is patterned by wet etching using a hydrochloric acid-based solution made of a mixture of hydrochloric acid and acetic acid as an etchant to form an electrode. Here, the mask pattern 44 is formed so that the conductive layer 40 formed on the upper surface of the ridge is not removed through the gap of the conductive layer 43 introduced earlier. As a result, the conductive layer 40 made of the Ni film remains on the upper surface of the ridge covered with the mask pattern 44, the side surface of the ridge, and the lower portion of the gap, and the Ni film is removed at the portion exposed from the mask pattern 44.
Thereafter, a semiconductor laser element is formed in the same manner as in the second embodiment. The obtained laser element has the same effect as the laser element of Example 1.

Example 6: Method for Manufacturing Nitride Semiconductor Laser Device In the method for manufacturing a laser device in this example, in the step (e) in the stacking of the conductive layers in Example 2, a conductive layer made of a Pt film corresponding to the shoulder of the ridge When the gap is introduced into the conductive layer 43, the conductive layer 43 corresponding to the shoulder portion of the ridge can be intensively sputtered without forming a mask pattern, and the conductive layer 43 is etched back. It can be manufactured in substantially the same manner as in Example 2 except that a gap is introduced into the layer 43. The obtained laser element has the same effect as the laser element of Example 1.
Examples of the intensive sputtering here include sputtering by Ar and sputtering by a gas in which chlorine or nitrogen is mixed with Ar.

Example 7: Nitride Semiconductor Laser Device As shown in FIG. 1B, the laser device of this example is an element that oscillates in the 500 nm band or less, and has the same laminated structure and ridge of nitride semiconductor layers as in Example 1. 14.
A first protective film 15 made of ZrO ₂ is formed on the surface of the p-side semiconductor layer excluding the upper surface of the ridge 14.
At a position corresponding to the base portion of the ridge 14, a gap 16 is disposed via the first protective film 15. The width of the void 16 (X in FIG. 2A (a)) is, for example, 400 nm, and the height H is about 110 nm.

Electrodes (17 and 18) are formed from the upper surface of the ridge 14 to a part on the nitride semiconductor layer on both sides of the ridge 14. The electrodes (17 and 18) have the same laminated structure as that of Example 1, and the p-side pad electrode 20 is formed on the electrodes (17 and 18).
A second protective film 19 is formed on the side surface of the nitride semiconductor layer and the exposed surface of the n-side semiconductor layer 11.
Further, an n-side electrode 21 is formed on the back surface of the substrate 10.
The nitride semiconductor laser element having such a gap also has the same effect as that of the first embodiment.
That is, the absorption of laser light by the electrode disposed thereon can be reduced in the extending direction of the ridge, and the driving current is reduced by about 15%, thereby showing a stable operating current and operating voltage for a long time.

Example 8: Manufacturing Method of Nitride Semiconductor Laser Element The laser element of Example 7 can be manufactured by the following method.
By controlling the film formation conditions of the first protective film, a first protective film 15 exposing the upper surface of the ridge is formed as shown in FIG. A conductive layer 40 made of a Ni film and a conductive layer 41 made of an Au film are formed in substantially the same manner as in Example 2. A mask pattern 42 is formed thereon as shown in FIG.
Thereafter, as shown in FIG. 7C, a conductive layer 43 made of a Pt film is formed, and the conductive layer 43 is patterned by a lift-off method (see FIG. 7D).
Although not shown, by forming a mask having an opening at a portion corresponding to the base portion of the ridge 14, a gap is formed at a position corresponding to the base portion of the ridge 14 of the conductive layer 43 as shown in FIG. 23 is introduced.

Subsequently, as shown in FIG. 7E, the conductive layer 41 made of an Au film is patterned by wet etching using the iodine iodide-based solution as an etchant using the conductive layer 43 as a mask. At this time, a part of the conductive layer 41 made of the Au film corresponding to the base portion of the ridge 14 is also removed through the gap of the conductive layer 43 introduced earlier, and voids are introduced into the portion. .
Thereafter, as shown in FIG. 7F, a mask pattern 44 covering the conductive layer 43 made of a Pt film is formed.

Using this mask pattern 44 as a mask, the conductive layer 40 made of a Ni film is patterned by wet etching using a hydrochloric acid-based solution made of a mixture of hydrochloric acid and acetic acid as an etchant to form an electrode. Here, the mask pattern 44 is formed so that the conductive layer 40 formed on the upper surface of the ridge is not removed through the gap of the conductive layer 43 introduced earlier. As a result, the conductive layer 40 made of the Ni film remains on the upper surface of the ridge covered with the mask pattern 44, the side surface of the ridge, and the lower portion of the gap, and the Ni film is removed at the portion exposed from the mask pattern 44.
Thereafter, a semiconductor laser element is formed in the same manner as in the second embodiment. The obtained laser element has the same effect as the laser element of Example 7.

  Even in this manufacturing method, after annealing to ensure ohmic properties, a part or all of the conductive layer 40 made of the Ni film adjacent to the gap 26b is unevenly distributed, and the first protective film 25 is exposed. Sites that are arranged in islands may be created. Further, the conductive layer 40 made of Ni film and the conductive layer 41 made of Au are alloyed, and these are partially or entirely arranged as a single layer structure, and an electrode structure as shown in FIG. 1A can be taken. There is a case.

Example 9: Nitride Semiconductor Laser Device and Manufacturing Method In this example, the steps (a) to (c) of Example 2 were substantially performed, and the first protective film in the step (d) was removed. By making the wet etching time using BHF longer than that in the second embodiment, for example, a void corresponding to the second void 16aa in (h) of FIG. 2B can be formed. Except for this, a semiconductor laser device is formed in substantially the same manner as in the second embodiment. The obtained laser element has the same effect as the laser element of Example 1.

  The nitride semiconductor laser device of the present invention can be used for optical disc applications, optical communication systems, printing machines, exposure applications, measurements, and the like. Further, it can be used as a bio-related excitation light source that can detect the presence or position of a substance by irradiating a substance having sensitivity at a specific wavelength with light obtained from a nitride semiconductor laser.

10 substrate 11 n-side semiconductor layer 12 active layer 13 p-side semiconductor layer 14 ridge 15, 25, 45, 55 first protective film 16, 16a, 16b, 26, 26a, 26b, 26b'36, 46, 56 void 16aa, 26bb Second gap 7, 17, 17a, 17b, 18, 27, 27a, 27b, 28, 37, 38, 47, 48, 57, 58, 67, 77 Electrode 19 Second protective film 20 Pad electrode 21 N side Electrodes 22, 23 Gap 40, 43, 50, 51, 53 Conductive layers 41, 43, 50, 51, 53 (Contains Au film) Conductive layers 43, 50, 51, 53 (Contains Pt film) Conductive layer 42, 44, 52 Mask pattern

Claims (9)

A substrate,
A nitride semiconductor layer stacked on the substrate and having a ridge on its surface;
A first protective film covering the nitride semiconductor layer;
A nitride semiconductor laser device having an electrode formed on said ridge and said first protective film,
The first protective film, before over cut Tsu di base portion and the ridge side faces, are disposed in contact with the nitride semiconductor layer and the part is,
Wherein a portion ranging ridge side faces from the ridge base portion of the first protective layer, a nitride semiconductor laser device, characterized in that it comprises a defined gap between the electrodes. The first protective layer is exposed to part of the side surface of the ridge, and the gap is spans the ridge side faces from the ridge base unit, according to claim 1 in contact with the ridge sides Nitride semiconductor laser device. The first protective film, a nitride semiconductor laser device according to claim 1 or 2 having a smaller refractive index than that of the nitride semiconductor layer. The gap is the nitride semiconductor laser device according to any one of claims 1 to 3 which are arranged substantially parallel to the ridge in the ridge extending direction. Wherein between the first protective film and the ridge, the nitride semiconductor laser device according to any one of claims 1-4 in which the second gap is disposed. (A) laminating a nitride semiconductor layer on a substrate;
(B) forming a mask pattern on the nitride semiconductor layer, and forming a ridge using the mask pattern;
(C) forming a first protective film on both side surfaces of the ridge, on the mask pattern, and on the nitride semiconductor layer exposed after the ridge formation;
(D) removing at least the mask pattern and the first protective film present on the mask pattern;
(E) A conductive layer composed of two or more multilayer films having different compositions is stacked on the nitride semiconductor layer including the ridge and the first protective film, and at least the shoulder of the outermost conductive layer from the base of the ridge. In the part corresponding to the part, a gap is partially introduced,
(F) forming an electrode by removing a part of the conductive layer through the gap and forming a gap defined by at least a portion of the first protective film extending from the ridge base to the ridge side surface and the conductive layer; And a method for manufacturing a nitride semiconductor laser device. The manufacturing method according to claim 6 , wherein the conductive layer is formed by a first conductive layer and a second conductive layer having an etching rate different from that of the first conductive layer disposed thereon. The conductive layer is formed by laminating a third conductive layer having an etching rate different from that of the first and second conductive layers under the first conductive layer,
After the step (f), a mask pattern is formed on the upper surface, the side surface of the ridge, and a partial surface of the nitride semiconductor layer on both sides of the ridge, and a part of the third conductive layer is removed using the mask pattern. The manufacturing method of Claim 7 including a process. The conductive layer is formed by laminating a third conductive layer having an etching rate different from that of the first and second conductive layers under the first conductive layer,
In the step (f), a part of the first conductive layer is removed to form a void,
Further, after the step (f), a mask pattern is formed on the upper surface, the side surface of the ridge, and a partial surface of the nitride semiconductor layer on both sides of the ridge, and the first conductive layer and the third conductive layer are formed using the mask pattern. The manufacturing method of Claim 7 including the process of removing a part of layer.

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